Titanium aluminide intermetallic composites

Abstract

An intermetallic composite and method of making an intermetallic composite is disclosed comprising a porous titanate preform of the formula εxTiyOz, where ε represents an element reduceable by molten aluminum to form an aluminate of the formula εiAjOk. Adding aluminum and heating the preform sufficient to melt the aluminum results in formation of a post-combustion intermetallic composite comprising both titanium aluminide and 68 -aluminate.

Description

FIELD OF THE INVENTION [0001] This invention relates to improvements in titanium aluminide intermetallic composites, and more particularly to improvements in titanium aluminide intermetallic composites suitable for use in automotive and aerospace applications. BACKGROUND OF THE INVENTION [0002] The production of titanium aluminide (“TiAl”) intermetallic matrix composites (“IMC”) (or simply Titanium Aluminide Composite “TAC”), has been studied by many academic and commercial organizations in recent years. Intermetallics are understood by those skilled in the art to mean binary alloys with phases in the mid-composition range. For example, binary alloys of titanium and aluminum can comprise the phases TiAl3, TiAl, or Ti3Al, or mixtures of these phases. Of these intermetallic phases, TiAl has relatively good mechanical properties for use as an engineering material, including high stiffness, strength, ductility and temperature resistance. The important crystal phases in an alloy are usua...

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Problems solved by technology

While this analysis suggests that this reaction can occur at room temperature, it has been found that combustion synthesis will not become fully activated until all of the aluminum has melted.

This suggests that there is a significant barrier in terms of kinetics preventing the TiO2 and aluminum from reacting once the preform has been infiltrated and prior to placing the material in a furnace at 850° C. Further, while the aluminum is certainly molten during the die casting process, the very nature of die casting removes heat from the material at such a high rate that the combustion reaction can not be initiated.

This increased porosity has a significant detrimental effect with regards to the mechanical properties of the material.

However, this advantage is negated by the significant difference in the cost of TiO compared to TiO2 (about ten times by weight), which essentially means the TAC produced using this oxide is cost-prohibitive for most applications.

While it is possible to reduce the total porosity in the TAC by including SAFFIL fiber, it is not possible to eliminate the porosity completely.

Therefore, for TAC materials based on TiO2 and Ti2O3, the inclusion of inert reinforcement materials has little practical commercial significance.

While this material represents a significant improvement over the composite produced using TiO2 (10.8% porosity), it is still cost-prohibitive with regards to many production applications, especially in the automotive industry.

Moreover, while 1.3% porosity is relatively small, it can still cause significant problems with regards to fatigue and fracture toughness in the high-temperature structural applications which these materials have been designed for.

While both methods may or may not result in a better performing material, neither achieves the original objective of producing a zero-porosity composite.

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